136ac495dSmrg<?xml version="1.0" encoding="UTF-8" standalone="no"?> 236ac495dSmrg<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Frequently Asked Questions</title><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="index.html" title="The GNU C++ Library" /><link rel="up" href="bk03.html" title="" /><link rel="prev" href="bk03.html" title="" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Frequently Asked Questions</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk03.html">Prev</a> </td><th width="60%" align="center"></th><td width="20%" align="right"> </td></tr></table><hr /></div><div class="article"><div class="titlepage"><div><div><h1 class="title"><a id="faq"></a>Frequently Asked Questions</h1></div><div><p class="copyright">Copyright © 3a2dc1f3fSmrg 2008-2018 436ac495dSmrg 5a2dc1f3fSmrg <a class="link" href="https://www.fsf.org" target="_top">FSF</a> 636ac495dSmrg </p></div></div><hr /></div><div class="qandaset"><a id="faq.faq"></a><dl><dt></dt><dd><dl><dt>1.1. <a href="faq.html#faq.what"> 736ac495dSmrg What is libstdc++? 836ac495dSmrg </a></dt><dt>1.2. <a href="faq.html#faq.why"> 936ac495dSmrg Why should I use libstdc++? 1036ac495dSmrg </a></dt><dt>1.3. <a href="faq.html#faq.who"> 1136ac495dSmrg Who's in charge of it? 1236ac495dSmrg </a></dt><dt>1.4. <a href="faq.html#faq.when"> 1336ac495dSmrg When is libstdc++ going to be finished? 1436ac495dSmrg </a></dt><dt>1.5. <a href="faq.html#faq.how"> 1536ac495dSmrg How do I contribute to the effort? 1636ac495dSmrg </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old"> 1736ac495dSmrg What happened to the older libg++? I need that! 1836ac495dSmrg </a></dt><dt>1.7. <a href="faq.html#faq.more_questions"> 1936ac495dSmrg What if I have more questions? 2036ac495dSmrg </a></dt></dl></dd><dt></dt><dd><dl><dt>2.1. <a href="faq.html#faq.license.what"> 2136ac495dSmrg What are the license terms for libstdc++? 2236ac495dSmrg </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program"> 2336ac495dSmrg So any program which uses libstdc++ falls under the GPL? 2436ac495dSmrg </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl"> 2536ac495dSmrg How is that different from the GNU {Lesser,Library} GPL? 2636ac495dSmrg </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions"> 2736ac495dSmrg I see. So, what restrictions are there on programs that use the library? 2836ac495dSmrg </a></dt></dl></dd><dt></dt><dd><dl><dt>3.1. <a href="faq.html#faq.how_to_install">How do I install libstdc++? 2936ac495dSmrg </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources? 3036ac495dSmrg </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works? 3136ac495dSmrg </a></dt><dt>3.4. <a href="faq.html#faq.how_to_set_paths">How do I insure that the dynamically linked library will be found? 3236ac495dSmrg </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx"> 3336ac495dSmrg What's libsupc++? 3436ac495dSmrg </a></dt><dt>3.6. <a href="faq.html#faq.size"> 3536ac495dSmrg This library is HUGE! 3636ac495dSmrg </a></dt></dl></dd><dt></dt><dd><dl><dt>4.1. <a href="faq.html#faq.other_compilers"> 3736ac495dSmrg Can libstdc++ be used with non-GNU compilers? 3836ac495dSmrg </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long"> 3936ac495dSmrg No 'long long' type on Solaris? 4036ac495dSmrg </a></dt><dt>4.3. <a href="faq.html#faq.predefined"> 4136ac495dSmrg _XOPEN_SOURCE and _GNU_SOURCE are always defined? 4236ac495dSmrg </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype"> 4336ac495dSmrg Mac OS X ctype.h is broken! How can I fix it? 4436ac495dSmrg </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386"> 4536ac495dSmrg Threading is broken on i386? 4636ac495dSmrg </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips"> 4736ac495dSmrg MIPS atomic operations 4836ac495dSmrg </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc"> 4936ac495dSmrg Recent GNU/Linux glibc required? 5036ac495dSmrg </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar"> 5136ac495dSmrg Can't use wchar_t/wstring on FreeBSD 5236ac495dSmrg </a></dt></dl></dd><dt></dt><dd><dl><dt>5.1. <a href="faq.html#faq.what_works"> 5336ac495dSmrg What works already? 5436ac495dSmrg </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs"> 5536ac495dSmrg Bugs in the ISO C++ language or library specification 5636ac495dSmrg </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs"> 5736ac495dSmrg Bugs in the compiler (gcc/g++) and not libstdc++ 5836ac495dSmrg </a></dt></dl></dd><dt></dt><dd><dl><dt>6.1. <a href="faq.html#faq.stream_reopening_fails"> 5936ac495dSmrg Reopening a stream fails 6036ac495dSmrg </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose"> 6136ac495dSmrg -Weffc++ complains too much 6236ac495dSmrg </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads"> 6336ac495dSmrg Ambiguous overloads after including an old-style header 6436ac495dSmrg </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers"> 6536ac495dSmrg The g++-3 headers are not ours 6636ac495dSmrg </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks"> 6736ac495dSmrg Errors about *Concept and 6836ac495dSmrg constraints in the STL 6936ac495dSmrg </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash"> 7036ac495dSmrg Program crashes when using library code in a 7136ac495dSmrg dynamically-loaded library 7236ac495dSmrg </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks"> 73a2dc1f3fSmrg “Memory leaks” in libstdc++ 7436ac495dSmrg </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on"> 7536ac495dSmrg list::size() is O(n)! 7636ac495dSmrg </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix"> 7736ac495dSmrg Aw, that's easy to fix! 7836ac495dSmrg </a></dt></dl></dd><dt></dt><dd><dl><dt>7.1. <a href="faq.html#faq.iterator_as_pod"> 79a2dc1f3fSmrg string::iterator is not char*; 80a2dc1f3fSmrg vector<T>::iterator is not T* 8136ac495dSmrg </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next"> 8236ac495dSmrg What's next after libstdc++? 8336ac495dSmrg </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl"> 8436ac495dSmrg What about the STL from SGI? 8536ac495dSmrg </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat"> 8636ac495dSmrg Extensions and Backward Compatibility 8736ac495dSmrg </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support"> 8836ac495dSmrg Does libstdc++ support TR1? 8936ac495dSmrg </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard? 9036ac495dSmrg </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi"> 9136ac495dSmrg What's an ABI and why is it so messy? 9236ac495dSmrg </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity"> 9336ac495dSmrg How do I make std::vector<T>::capacity() == std::vector<T>::size? 9436ac495dSmrg </a></dt></dl></dd></dl><table border="0" style="width: 100%;"><colgroup><col align="left" width="1%" /><col /></colgroup><tbody><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>1.1. <a href="faq.html#faq.what"> 9536ac495dSmrg What is libstdc++? 9636ac495dSmrg </a></dt><dt>1.2. <a href="faq.html#faq.why"> 9736ac495dSmrg Why should I use libstdc++? 9836ac495dSmrg </a></dt><dt>1.3. <a href="faq.html#faq.who"> 9936ac495dSmrg Who's in charge of it? 10036ac495dSmrg </a></dt><dt>1.4. <a href="faq.html#faq.when"> 10136ac495dSmrg When is libstdc++ going to be finished? 10236ac495dSmrg </a></dt><dt>1.5. <a href="faq.html#faq.how"> 10336ac495dSmrg How do I contribute to the effort? 10436ac495dSmrg </a></dt><dt>1.6. <a href="faq.html#faq.whereis_old"> 10536ac495dSmrg What happened to the older libg++? I need that! 10636ac495dSmrg </a></dt><dt>1.7. <a href="faq.html#faq.more_questions"> 10736ac495dSmrg What if I have more questions? 10836ac495dSmrg </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.what"></a><a id="faq.what.q"></a><p><strong>1.1.</strong></p></td><td align="left" valign="top"><p> 10936ac495dSmrg What is libstdc++? 11036ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="faq.what.a"></a></td><td align="left" valign="top"><p> 11136ac495dSmrg The GNU Standard C++ Library v3 is an ongoing project to 112a2dc1f3fSmrg implement the ISO 14882 C++ Standard Library as described in 113a2dc1f3fSmrg clauses 20 through 33 and annex D (prior to the 2017 standard 114a2dc1f3fSmrg the library clauses started with 17). For those who want to see 11536ac495dSmrg exactly how far the project has come, or just want the latest 116a2dc1f3fSmrg bleeding-edge code, the up-to-date source can be cloned via 117a2dc1f3fSmrg <a class="link" href="https://gcc.gnu.org/git.html" target="_top">Git</a>. 118a2dc1f3fSmrg </p><p> 119a2dc1f3fSmrg N.B. The library is called libstdc++ <span class="emphasis"><em>not</em></span> stdlibc++. 12036ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.why"></a><a id="q-why"></a><p><strong>1.2.</strong></p></td><td align="left" valign="top"><p> 12136ac495dSmrg Why should I use libstdc++? 12236ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-why"></a></td><td align="left" valign="top"><p> 12336ac495dSmrg The completion of the initial ISO C++ standardization effort gave the C++ 12436ac495dSmrg community a powerful set of reuseable tools in the form of the C++ 12536ac495dSmrg Standard Library. However, for several years C++ implementations were 12636ac495dSmrg (as the Draft Standard used to say) <span class="quote">“<span class="quote">incomplet and 12736ac495dSmrg incorrekt</span>”</span>, and many suffered from limitations of the compilers 12836ac495dSmrg that used them. 12936ac495dSmrg </p><p> 13036ac495dSmrg The GNU compiler collection 13136ac495dSmrg (<span class="command"><strong>gcc</strong></span>, <span class="command"><strong>g++</strong></span>, etc) is widely 13236ac495dSmrg considered to be one of the leading compilers in the world. Its 13336ac495dSmrg development is overseen by the 13436ac495dSmrg <a class="link" href="https://gcc.gnu.org/" target="_top">GCC team</a>. All of 13536ac495dSmrg the rapid development and near-legendary 13636ac495dSmrg <a class="link" href="https://gcc.gnu.org/buildstat.html" target="_top">portability</a> 13736ac495dSmrg that are the hallmarks of an open-source project are applied to libstdc++. 13836ac495dSmrg </p><p> 139a2dc1f3fSmrg All of the standard classes and functions from C++98/C++03, C++11 and C++14 14036ac495dSmrg (such as <code class="classname">string</code>, 14136ac495dSmrg <code class="classname">vector<></code>, iostreams, algorithms etc.) 142a2dc1f3fSmrg are freely available and attempt to be fully compliant. 14336ac495dSmrg Work is ongoing to complete support for the current revision of the 14436ac495dSmrg ISO C++ Standard. 14536ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.who"></a><a id="q-who"></a><p><strong>1.3.</strong></p></td><td align="left" valign="top"><p> 14636ac495dSmrg Who's in charge of it? 14736ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-who"></a></td><td align="left" valign="top"><p> 14836ac495dSmrg The libstdc++ project is contributed to by several developers 14936ac495dSmrg all over the world, in the same way as GCC or the Linux kernel. 15036ac495dSmrg The current maintainers are listed in the 15136ac495dSmrg <a class="link" href="https://gcc.gnu.org/viewcvs/gcc/trunk/MAINTAINERS?view=co" target="_top"><code class="filename">MAINTAINERS</code></a> 15236ac495dSmrg file (look for "c++ runtime libs"). 15336ac495dSmrg </p><p> 15436ac495dSmrg Development and discussion is held on the libstdc++ mailing 15536ac495dSmrg list. Subscribing to the list, or searching the list 15636ac495dSmrg archives, is open to everyone. You can read instructions for 15736ac495dSmrg doing so on the <a class="link" href="https://gcc.gnu.org/lists.html" target="_top">GCC mailing lists</a> page. 15836ac495dSmrg If you have questions, ideas, code, or are just curious, sign up! 15936ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.when"></a><a id="q-when"></a><p><strong>1.4.</strong></p></td><td align="left" valign="top"><p> 16036ac495dSmrg When is libstdc++ going to be finished? 16136ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-when"></a></td><td align="left" valign="top"><p> 16236ac495dSmrg Nathan Myers gave the best of all possible answers, responding to 16336ac495dSmrg a Usenet article asking this question: <span class="emphasis"><em>Sooner, if you 16436ac495dSmrg help.</em></span> 16536ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how"></a><a id="q-how"></a><p><strong>1.5.</strong></p></td><td align="left" valign="top"><p> 16636ac495dSmrg How do I contribute to the effort? 16736ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how"></a></td><td align="left" valign="top"><p> 16836ac495dSmrg See the <a class="link" href="manual/appendix_contributing.html" title="Appendix A. Contributing">Contributing</a> section in 16936ac495dSmrg the manual. Subscribing to the mailing list (see above, or 17036ac495dSmrg the homepage) is a very good idea if you have something to 17136ac495dSmrg contribute, or if you have spare time and want to 17236ac495dSmrg help. Contributions don't have to be in the form of source code; 17336ac495dSmrg anybody who is willing to help write documentation, for example, 17436ac495dSmrg or has found a bug in code that we all thought was working and is 17536ac495dSmrg willing to provide details, is more than welcome! 17636ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.whereis_old"></a><a id="q-whereis_old"></a><p><strong>1.6.</strong></p></td><td align="left" valign="top"><p> 17736ac495dSmrg What happened to the older libg++? I need that! 17836ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-whereis_old"></a></td><td align="left" valign="top"><p> 17936ac495dSmrg The last libg++ README states 18036ac495dSmrg <span class="quote">“<span class="quote">This package is considered obsolete and is no longer 18136ac495dSmrg being developed.</span>”</span> 18236ac495dSmrg It should not be used for new projects, and won't even compile with 18336ac495dSmrg recent releases of GCC (or most other C++ compilers). 18436ac495dSmrg </p><p> 18536ac495dSmrg More information can be found in the 18636ac495dSmrg <a class="link" href="manual/backwards.html" title="Backwards Compatibility">Backwards 18736ac495dSmrg Compatibility</a> section of the libstdc++ manual. 18836ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.more_questions"></a><a id="q-more_questions"></a><p><strong>1.7.</strong></p></td><td align="left" valign="top"><p> 18936ac495dSmrg What if I have more questions? 19036ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-more_questions"></a></td><td align="left" valign="top"><p> 19136ac495dSmrg If you have read the documentation, and your question remains 19236ac495dSmrg unanswered, then just ask the mailing list. At present, you do not 19336ac495dSmrg need to be subscribed to the list to send a message to it. More 19436ac495dSmrg information is available on the homepage (including how to browse 19536ac495dSmrg the list archives); to send a message to the list, 19636ac495dSmrg use <code class="email"><<a class="email" href="mailto:libstdc++@gcc.gnu.org">libstdc++@gcc.gnu.org</a>></code>. 19736ac495dSmrg </p><p> 19836ac495dSmrg If you have a question that you think should be included 19936ac495dSmrg here, or if you have a question <span class="emphasis"><em>about</em></span> a question/answer 20036ac495dSmrg here, please send email to the libstdc++ mailing list, as above. 20136ac495dSmrg </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>2.1. <a href="faq.html#faq.license.what"> 20236ac495dSmrg What are the license terms for libstdc++? 20336ac495dSmrg </a></dt><dt>2.2. <a href="faq.html#faq.license.any_program"> 20436ac495dSmrg So any program which uses libstdc++ falls under the GPL? 20536ac495dSmrg </a></dt><dt>2.3. <a href="faq.html#faq.license.lgpl"> 20636ac495dSmrg How is that different from the GNU {Lesser,Library} GPL? 20736ac495dSmrg </a></dt><dt>2.4. <a href="faq.html#faq.license.what_restrictions"> 20836ac495dSmrg I see. So, what restrictions are there on programs that use the library? 20936ac495dSmrg </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.license.what"></a><a id="q-license.what"></a><p><strong>2.1.</strong></p></td><td align="left" valign="top"><p> 21036ac495dSmrg What are the license terms for libstdc++? 21136ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.what"></a></td><td align="left" valign="top"><p> 21236ac495dSmrg See <a class="link" href="manual/license.html" title="License">our license description</a> 21336ac495dSmrg for these and related questions. 21436ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.license.any_program"></a><a id="q-license.any_program"></a><p><strong>2.2.</strong></p></td><td align="left" valign="top"><p> 21536ac495dSmrg So any program which uses libstdc++ falls under the GPL? 21636ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.any_program"></a></td><td align="left" valign="top"><p> 21736ac495dSmrg No. The special exception permits use of the library in 21836ac495dSmrg proprietary applications. 21936ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.license.lgpl"></a><a id="q-license.lgpl"></a><p><strong>2.3.</strong></p></td><td align="left" valign="top"><p> 22036ac495dSmrg How is that different from the GNU {Lesser,Library} GPL? 22136ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.lgpl"></a></td><td align="left" valign="top"><p> 22236ac495dSmrg The LGPL requires that users be able to replace the LGPL code with a 22336ac495dSmrg modified version; this is trivial if the library in question is a C 22436ac495dSmrg shared library. But there's no way to make that work with C++, where 22536ac495dSmrg much of the library consists of inline functions and templates, which 22636ac495dSmrg are expanded inside the code that uses the library. So to allow people 22736ac495dSmrg to replace the library code, someone using the library would have to 22836ac495dSmrg distribute their own source, rendering the LGPL equivalent to the GPL. 22936ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.license.what_restrictions"></a><a id="q-license.what_restrictions"></a><p><strong>2.4.</strong></p></td><td align="left" valign="top"><p> 23036ac495dSmrg I see. So, what restrictions are there on programs that use the library? 23136ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-license.what_restrictions"></a></td><td align="left" valign="top"><p> 23236ac495dSmrg None. We encourage such programs to be released as free software, 23336ac495dSmrg but we won't punish you or sue you if you choose otherwise. 23436ac495dSmrg </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>3.1. <a href="faq.html#faq.how_to_install">How do I install libstdc++? 23536ac495dSmrg </a></dt><dt>3.2. <a href="faq.html#faq.how_to_get_sources">How does one get current libstdc++ sources? 23636ac495dSmrg </a></dt><dt>3.3. <a href="faq.html#faq.how_to_test">How do I know if it works? 23736ac495dSmrg </a></dt><dt>3.4. <a href="faq.html#faq.how_to_set_paths">How do I insure that the dynamically linked library will be found? 23836ac495dSmrg </a></dt><dt>3.5. <a href="faq.html#faq.what_is_libsupcxx"> 23936ac495dSmrg What's libsupc++? 24036ac495dSmrg </a></dt><dt>3.6. <a href="faq.html#faq.size"> 24136ac495dSmrg This library is HUGE! 24236ac495dSmrg </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how_to_install"></a><a id="q-how_to_install"></a><p><strong>3.1.</strong></p></td><td align="left" valign="top"><p>How do I install libstdc++? 24336ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how_to_install"></a></td><td align="left" valign="top"><p> 24436ac495dSmrg Often libstdc++ comes pre-installed as an integral part of many 24536ac495dSmrg existing GNU/Linux and Unix systems, as well as many embedded 24636ac495dSmrg development tools. It may be necessary to install extra 24736ac495dSmrg development packages to get the headers, or the documentation, or 24836ac495dSmrg the source: please consult your vendor for details. 24936ac495dSmrg </p><p> 25036ac495dSmrg To build and install from the GNU GCC sources, please consult the 25136ac495dSmrg <a class="link" href="manual/setup.html" title="Chapter 2. Setup">setup 25236ac495dSmrg documentation</a> for detailed 25336ac495dSmrg instructions. You may wish to browse those files ahead 25436ac495dSmrg of time to get a feel for what's required. 25536ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how_to_get_sources"></a><a id="q-how_to_get_sources"></a><p><strong>3.2.</strong></p></td><td align="left" valign="top"><p>How does one get current libstdc++ sources? 25636ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how_to_get_sources"></a></td><td align="left" valign="top"><p> 25736ac495dSmrg Libstdc++ sources for all official releases can be obtained as 25836ac495dSmrg part of the GCC sources, available from various sites and 25936ac495dSmrg mirrors. A full <a class="link" href="https://gcc.gnu.org/mirrors.html" target="_top">list of 26036ac495dSmrg download sites</a> is provided on the main GCC site. 26136ac495dSmrg </p><p> 262a2dc1f3fSmrg Current libstdc++ sources can always be found in the main GCC source 263a2dc1f3fSmrg repository, available using the appropriate version control tool. 264a2dc1f3fSmrg At this time, that tool is <span class="application">Git</span>. 265a2dc1f3fSmrg For more details see the documentation on 266a2dc1f3fSmrg <a class="link" href="https://gcc.gnu.org/git.html" target="_top">using the Git repository</a>. 26736ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how_to_test"></a><a id="q-how_to_test"></a><p><strong>3.3.</strong></p></td><td align="left" valign="top"><p>How do I know if it works? 26836ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how_to_test"></a></td><td align="left" valign="top"><p> 26936ac495dSmrg Libstdc++ comes with its own validation testsuite, which includes 27036ac495dSmrg conformance testing, regression testing, ABI testing, and 27136ac495dSmrg performance testing. Please consult the 27236ac495dSmrg <a class="link" href="http://gcc.gnu.org/install/test.html" target="_top">testing 27336ac495dSmrg documentation</a> for GCC and 27436ac495dSmrg <a class="link" href="manual/test.html" title="Testing">Testing</a> in the libstdc++ 27536ac495dSmrg manual for more details. 27636ac495dSmrg </p><p> 27736ac495dSmrg If you find bugs in the testsuite programs themselves, or if you 27836ac495dSmrg think of a new test program that should be added to the suite, 27936ac495dSmrg <span class="emphasis"><em>please</em></span> write up your idea and send it to the list! 28036ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.how_to_set_paths"></a><a id="q-how_to_set_paths"></a><p><strong>3.4.</strong></p></td><td align="left" valign="top"><p>How do I insure that the dynamically linked library will be found? 28136ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-how_to_set_paths"></a></td><td align="left" valign="top"><p> 28236ac495dSmrg Depending on your platform and library version, the error message might 28336ac495dSmrg be similar to one of the following: 28436ac495dSmrg </p><pre class="screen"> 28536ac495dSmrg ./a.out: error while loading shared libraries: libstdc++.so.6: cannot open shared object file: No such file or directory 28636ac495dSmrg 28736ac495dSmrg /usr/libexec/ld-elf.so.1: Shared object "libstdc++.so.6" not found 28836ac495dSmrg </pre><p> 28936ac495dSmrg This doesn't mean that the shared library isn't installed, only 29036ac495dSmrg that the dynamic linker can't find it. When a dynamically-linked 29136ac495dSmrg executable is run the linker finds and loads the required shared 29236ac495dSmrg libraries by searching a pre-configured list of directories. If 29336ac495dSmrg the directory where you've installed libstdc++ is not in this list 29436ac495dSmrg then the libraries won't be found. 29536ac495dSmrg </p><p> 29636ac495dSmrg If you already have an older version of libstdc++ installed then the 29736ac495dSmrg error might look like one of the following instead: 29836ac495dSmrg </p><pre class="screen"> 29936ac495dSmrg ./a.out: /usr/lib/libstdc++.so.6: version `GLIBCXX_3.4.20' not found 30036ac495dSmrg ./a.out: /usr/lib/libstdc++.so.6: version `CXXABI_1.3.8' not found 30136ac495dSmrg </pre><p> 30236ac495dSmrg This means the linker found <code class="filename">/usr/lib/libstdc++.so.6</code> 30336ac495dSmrg but that library belongs to an older version of GCC than was used to 30436ac495dSmrg compile and link the program <code class="filename">a.out</code> (or some part 30536ac495dSmrg of it). The program depends on code defined in the newer libstdc++ 30636ac495dSmrg that belongs to the newer version of GCC, so the linker must be told 30736ac495dSmrg how to find the newer libstdc++ shared library. 30836ac495dSmrg </p><p> 30936ac495dSmrg The simplest way to fix this is 31036ac495dSmrg to use the <code class="envar">LD_LIBRARY_PATH</code> environment variable, 31136ac495dSmrg which is a colon-separated list of directories in which the linker 31236ac495dSmrg will search for shared libraries: 31336ac495dSmrg </p><pre class="screen"><span class="command"><strong> 31436ac495dSmrg export LD_LIBRARY_PATH=${prefix}/lib:$LD_LIBRARY_PATH 31536ac495dSmrg </strong></span></pre><p> 31636ac495dSmrg Here the shell variable <code class="varname">${prefix}</code> is assumed to contain 31736ac495dSmrg the directory prefix where GCC was installed to. The directory containing 31836ac495dSmrg the library might depend on whether you want the 32-bit or 64-bit copy 31936ac495dSmrg of the library, so for example would be 32036ac495dSmrg <code class="filename">${prefix}/lib64</code> on some systems. 32136ac495dSmrg The exact environment variable to use will depend on your 32236ac495dSmrg platform, e.g. <code class="envar">DYLD_LIBRARY_PATH</code> for Darwin, 32336ac495dSmrg <code class="envar">LD_LIBRARY_PATH_32</code>/<code class="envar">LD_LIBRARY_PATH_64</code> 32436ac495dSmrg for Solaris 32-/64-bit, 32536ac495dSmrg and <code class="envar">SHLIB_PATH</code> for HP-UX. 32636ac495dSmrg </p><p> 32736ac495dSmrg See the man pages for <span class="command"><strong>ld</strong></span>, <span class="command"><strong>ldd</strong></span> 32836ac495dSmrg and <span class="command"><strong>ldconfig</strong></span> for more information. The dynamic 32936ac495dSmrg linker has different names on different platforms but the man page 33036ac495dSmrg is usually called something such as <code class="filename">ld.so</code>, 33136ac495dSmrg <code class="filename">rtld</code> or <code class="filename">dld.so</code>. 33236ac495dSmrg </p><p> 33336ac495dSmrg Using <code class="envar">LD_LIBRARY_PATH</code> is not always the best solution, 33436ac495dSmrg <a class="link" href="manual/using_dynamic_or_shared.html#manual.intro.using.linkage.dynamic" title="Finding Dynamic or Shared Libraries">Finding Dynamic or Shared 33536ac495dSmrg Libraries</a> in the manual gives some alternatives. 33636ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.what_is_libsupcxx"></a><a id="q-what_is_libsupcxx"></a><p><strong>3.5.</strong></p></td><td align="left" valign="top"><p> 33736ac495dSmrg What's libsupc++? 33836ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_is_libsupcxx"></a></td><td align="left" valign="top"><p> 33936ac495dSmrg If the only functions from <code class="filename">libstdc++.a</code> 34036ac495dSmrg which you need are language support functions (those listed in 34136ac495dSmrg <a class="link" href="manual/support.html" title="Chapter 4. Support">clause 18</a> of the 34236ac495dSmrg standard, e.g., <code class="function">new</code> and 34336ac495dSmrg <code class="function">delete</code>), then try linking against 34436ac495dSmrg <code class="filename">libsupc++.a</code>, which is a subset of 34536ac495dSmrg <code class="filename">libstdc++.a</code>. (Using <span class="command"><strong>gcc</strong></span> 34636ac495dSmrg instead of <span class="command"><strong>g++</strong></span> and explicitly linking in 34736ac495dSmrg <code class="filename">libsupc++.a</code> via <code class="option">-lsupc++</code> 34836ac495dSmrg for the final link step will do it). This library contains only 34936ac495dSmrg those support routines, one per object file. But if you are 35036ac495dSmrg using anything from the rest of the library, such as IOStreams 35136ac495dSmrg or vectors, then you'll still need pieces from 35236ac495dSmrg <code class="filename">libstdc++.a</code>. 35336ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.size"></a><a id="q-size"></a><p><strong>3.6.</strong></p></td><td align="left" valign="top"><p> 35436ac495dSmrg This library is HUGE! 35536ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size"></a></td><td align="left" valign="top"><p> 35636ac495dSmrg Usually the size of libraries on disk isn't noticeable. When a 35736ac495dSmrg link editor (or simply <span class="quote">“<span class="quote">linker</span>”</span>) pulls things from a 35836ac495dSmrg static archive library, only the necessary object files are copied 35936ac495dSmrg into your executable, not the entire library. Unfortunately, even 36036ac495dSmrg if you only need a single function or variable from an object file, 36136ac495dSmrg the entire object file is extracted. (There's nothing unique to C++ 36236ac495dSmrg or libstdc++ about this; it's just common behavior, given here 36336ac495dSmrg for background reasons.) 36436ac495dSmrg </p><p> 36536ac495dSmrg Some of the object files which make up 36636ac495dSmrg <code class="filename">libstdc++.a</code> are rather large. 36736ac495dSmrg If you create a statically-linked executable with 36836ac495dSmrg <code class="option">-static</code>, those large object files are suddenly part 36936ac495dSmrg of your executable. Historically the best way around this was to 37036ac495dSmrg only place a very few functions (often only a single one) in each 37136ac495dSmrg source/object file; then extracting a single function is the same 37236ac495dSmrg as extracting a single <code class="filename">.o</code> file. For libstdc++ this 37336ac495dSmrg is only possible to a certain extent; the object files in question contain 37436ac495dSmrg template classes and template functions, pre-instantiated, and 37536ac495dSmrg splitting those up causes severe maintenance headaches. 37636ac495dSmrg </p><p> 37736ac495dSmrg On supported platforms, libstdc++ takes advantage of garbage 37836ac495dSmrg collection in the GNU linker to get a result similar to separating 37936ac495dSmrg each symbol into a separate source and object files. On these platforms, 38036ac495dSmrg GNU ld can place each function and variable into its own 38136ac495dSmrg section in a <code class="filename">.o</code> file. The GNU linker can then perform 38236ac495dSmrg garbage collection on unused sections; this reduces the situation to only 38336ac495dSmrg copying needed functions into the executable, as before, but all 38436ac495dSmrg happens automatically. 38536ac495dSmrg </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>4.1. <a href="faq.html#faq.other_compilers"> 38636ac495dSmrg Can libstdc++ be used with non-GNU compilers? 38736ac495dSmrg </a></dt><dt>4.2. <a href="faq.html#faq.solaris_long_long"> 38836ac495dSmrg No 'long long' type on Solaris? 38936ac495dSmrg </a></dt><dt>4.3. <a href="faq.html#faq.predefined"> 39036ac495dSmrg _XOPEN_SOURCE and _GNU_SOURCE are always defined? 39136ac495dSmrg </a></dt><dt>4.4. <a href="faq.html#faq.darwin_ctype"> 39236ac495dSmrg Mac OS X ctype.h is broken! How can I fix it? 39336ac495dSmrg </a></dt><dt>4.5. <a href="faq.html#faq.threads_i386"> 39436ac495dSmrg Threading is broken on i386? 39536ac495dSmrg </a></dt><dt>4.6. <a href="faq.html#faq.atomic_mips"> 39636ac495dSmrg MIPS atomic operations 39736ac495dSmrg </a></dt><dt>4.7. <a href="faq.html#faq.linux_glibc"> 39836ac495dSmrg Recent GNU/Linux glibc required? 39936ac495dSmrg </a></dt><dt>4.8. <a href="faq.html#faq.freebsd_wchar"> 40036ac495dSmrg Can't use wchar_t/wstring on FreeBSD 40136ac495dSmrg </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.other_compilers"></a><a id="q-other_compilers"></a><p><strong>4.1.</strong></p></td><td align="left" valign="top"><p> 40236ac495dSmrg Can libstdc++ be used with non-GNU compilers? 40336ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-other_compilers"></a></td><td align="left" valign="top"><p> 40436ac495dSmrg Perhaps. 40536ac495dSmrg </p><p> 40636ac495dSmrg Since the goal of ISO Standardization is for all C++ 40736ac495dSmrg implementations to be able to share code, libstdc++ should be 40836ac495dSmrg usable under any ISO-compliant compiler, at least in theory. 40936ac495dSmrg </p><p> 41036ac495dSmrg However, the reality is that libstdc++ is targeted and optimized 41136ac495dSmrg for GCC/G++. This means that often libstdc++ uses specific, 41236ac495dSmrg non-standard features of G++ that are not present in older 41336ac495dSmrg versions of proprietary compilers. It may take as much as a year or two 41436ac495dSmrg after an official release of GCC that contains these features for 41536ac495dSmrg proprietary tools to support these constructs. 41636ac495dSmrg </p><p> 41736ac495dSmrg Recent versions of libstdc++ are known to work with the Clang compiler. 41836ac495dSmrg In the near past, specific released versions of libstdc++ have 41936ac495dSmrg been known to work with versions of the EDG C++ compiler, and 42036ac495dSmrg vendor-specific proprietary C++ compilers such as the Intel ICC 42136ac495dSmrg C++ compiler. 42236ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.solaris_long_long"></a><a id="q-solaris_long_long"></a><p><strong>4.2.</strong></p></td><td align="left" valign="top"><p> 42336ac495dSmrg No '<span class="type">long long</span>' type on Solaris? 424a2dc1f3fSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-solaris_long_long"></a></td><td align="left" valign="top"><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This answer is old and probably no longer be relevant.</p></div><p> 42536ac495dSmrg By default we try to support the C99 <span class="type">long long</span> type. 42636ac495dSmrg This requires that certain functions from your C library be present. 42736ac495dSmrg </p><p> 42836ac495dSmrg Up through release 3.0.2 the platform-specific tests performed by 42936ac495dSmrg libstdc++ were too general, resulting in a conservative approach 43036ac495dSmrg to enabling the <span class="type">long long</span> code paths. The most 43136ac495dSmrg commonly reported platform affected was Solaris. 43236ac495dSmrg </p><p> 43336ac495dSmrg This has been fixed for libstdc++ releases greater than 3.0.3. 43436ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.predefined"></a><a id="q-predefined"></a><p><strong>4.3.</strong></p></td><td align="left" valign="top"><p> 43536ac495dSmrg <code class="constant">_XOPEN_SOURCE</code> and <code class="constant">_GNU_SOURCE</code> are always defined? 43636ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-predefined"></a></td><td align="left" valign="top"><p>On Solaris, <span class="command"><strong>g++</strong></span> (but not <span class="command"><strong>gcc</strong></span>) 43736ac495dSmrg always defines the preprocessor macro 43836ac495dSmrg <code class="constant">_XOPEN_SOURCE</code>. On GNU/Linux, the same happens 43936ac495dSmrg with <code class="constant">_GNU_SOURCE</code>. (This is not an exhaustive list; 44036ac495dSmrg other macros and other platforms are also affected.) 44136ac495dSmrg </p><p>These macros are typically used in C library headers, guarding new 44236ac495dSmrg versions of functions from their older versions. The C++98 standard 44336ac495dSmrg library includes the C standard library, but it requires the C90 44436ac495dSmrg version, which for backwards-compatibility reasons is often not the 44536ac495dSmrg default for many vendors. 44636ac495dSmrg </p><p>More to the point, the C++ standard requires behavior which is only 44736ac495dSmrg available on certain platforms after certain symbols are defined. 44836ac495dSmrg Usually the issue involves I/O-related typedefs. In order to 44936ac495dSmrg ensure correctness, the compiler simply predefines those symbols. 45036ac495dSmrg </p><p>Note that it's not enough to <code class="literal">#define</code> them only when the library is 45136ac495dSmrg being built (during installation). Since we don't have an 'export' 45236ac495dSmrg keyword, much of the library exists as headers, which means that 45336ac495dSmrg the symbols must also be defined as your programs are parsed and 45436ac495dSmrg compiled. 45536ac495dSmrg </p><p>To see which symbols are defined, look for 45636ac495dSmrg <code class="varname">CPLUSPLUS_CPP_SPEC</code> in 45736ac495dSmrg the gcc config headers for your target (and try changing them to 45836ac495dSmrg see what happens when building complicated code). You can also run 459*8feb0f0bSmrg <span class="command"><strong>g++ -E -dM -x c++ /dev/null</strong></span> to display 46036ac495dSmrg a list of predefined macros for any particular installation. 46136ac495dSmrg </p><p>This has been discussed on the mailing lists 46236ac495dSmrg <a class="link" href="http://gcc.gnu.org/cgi-bin/htsearch?method=and&format=builtin-long&sort=score&words=_XOPEN_SOURCE+Solaris" target="_top">quite a bit</a>. 46336ac495dSmrg </p><p>This method is something of a wart. We'd like to find a cleaner 46436ac495dSmrg solution, but nobody yet has contributed the time. 46536ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.darwin_ctype"></a><a id="q-darwin_ctype"></a><p><strong>4.4.</strong></p></td><td align="left" valign="top"><p> 46636ac495dSmrg Mac OS X <code class="filename">ctype.h</code> is broken! How can I fix it? 46736ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-darwin_ctype"></a></td><td align="left" valign="top"><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This answer is old and probably no longer be relevant.</p></div><p> 46836ac495dSmrg This was a long-standing bug in the OS X support. Fortunately, the 46936ac495dSmrg <a class="link" href="http://gcc.gnu.org/ml/gcc/2002-03/msg00817.html" target="_top">patch</a> 47036ac495dSmrg was quite simple, and well-known. 47136ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.threads_i386"></a><a id="q-threads_i386"></a><p><strong>4.5.</strong></p></td><td align="left" valign="top"><p> 47236ac495dSmrg Threading is broken on i386? 47336ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-threads_i386"></a></td><td align="left" valign="top"><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This answer is old and probably no longer be relevant.</p></div><p>Support for atomic integer operations was broken on i386 47436ac495dSmrg platforms. The assembly code accidentally used opcodes that are 47536ac495dSmrg only available on the i486 and later. So if you configured GCC 47636ac495dSmrg to target, for example, i386-linux, but actually used the programs 47736ac495dSmrg on an i686, then you would encounter no problems. Only when 47836ac495dSmrg actually running the code on a i386 will the problem appear. 47936ac495dSmrg </p><p>This is fixed in 3.2.2. 48036ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.atomic_mips"></a><a id="q-atomic_mips"></a><p><strong>4.6.</strong></p></td><td align="left" valign="top"><p> 48136ac495dSmrg MIPS atomic operations 48236ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-atomic_mips"></a></td><td align="left" valign="top"><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This answer is old and probably no longer be relevant.</p></div><p> 48336ac495dSmrg The atomic locking routines for MIPS targets requires MIPS II 48436ac495dSmrg and later. A patch went in just after the 3.3 release to 48536ac495dSmrg make mips* use the generic implementation instead. You can also 48636ac495dSmrg configure for mipsel-elf as a workaround. 48736ac495dSmrg </p><p> 48836ac495dSmrg The mips*-*-linux* port continues to use the MIPS II routines, and more 48936ac495dSmrg work in this area is expected. 49036ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.linux_glibc"></a><a id="q-linux_glibc"></a><p><strong>4.7.</strong></p></td><td align="left" valign="top"><p> 49136ac495dSmrg Recent GNU/Linux glibc required? 49236ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-linux_glibc"></a></td><td align="left" valign="top"><p>When running on GNU/Linux, libstdc++ 3.2.1 (shared library version 49336ac495dSmrg 5.0.1) and later uses localization and formatting code from the system 49436ac495dSmrg C library (glibc) version 2.2.5 which contains necessary bugfixes. 49536ac495dSmrg All GNU/Linux distros make more recent versions available now. 49636ac495dSmrg libstdc++ 4.6.0 and later require glibc 2.3 or later for this 49736ac495dSmrg localization and formatting code. 49836ac495dSmrg </p><p>The guideline is simple: the more recent the C++ library, the 49936ac495dSmrg more recent the C library. (This is also documented in the main 50036ac495dSmrg GCC installation instructions.) 50136ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.freebsd_wchar"></a><a id="q-freebsd_wchar"></a><p><strong>4.8.</strong></p></td><td align="left" valign="top"><p> 502a2dc1f3fSmrg Can't use <span class="type">wchar_t</span>/<code class="classname">wstring</code> on FreeBSD 50336ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-freebsd_wchar"></a></td><td align="left" valign="top"><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This answer is old and probably no longer be relevant.</p></div><p> 50436ac495dSmrg Older versions of FreeBSD's C library do not have sufficient 50536ac495dSmrg support for wide character functions, and as a result the 50636ac495dSmrg libstdc++ configury decides that <span class="type">wchar_t</span> support should be 50736ac495dSmrg disabled. In addition, the libstdc++ platform checks that 50836ac495dSmrg enabled <span class="type">wchar_t</span> were quite strict, and not granular 50936ac495dSmrg enough to detect when the minimal support to 51036ac495dSmrg enable <span class="type">wchar_t</span> and C++ library structures 51136ac495dSmrg like <code class="classname">wstring</code> were present. This impacted Solaris, 51236ac495dSmrg Darwin, and BSD variants, and is fixed in libstdc++ versions post 4.1.0. 51336ac495dSmrg </p><p> 51436ac495dSmrg </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>5.1. <a href="faq.html#faq.what_works"> 51536ac495dSmrg What works already? 51636ac495dSmrg </a></dt><dt>5.2. <a href="faq.html#faq.standard_bugs"> 51736ac495dSmrg Bugs in the ISO C++ language or library specification 51836ac495dSmrg </a></dt><dt>5.3. <a href="faq.html#faq.compiler_bugs"> 51936ac495dSmrg Bugs in the compiler (gcc/g++) and not libstdc++ 52036ac495dSmrg </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.what_works"></a><a id="q-what_works"></a><p><strong>5.1.</strong></p></td><td align="left" valign="top"><p> 52136ac495dSmrg What works already? 52236ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_works"></a></td><td align="left" valign="top"><p> 52336ac495dSmrg Short answer: Pretty much everything <span class="emphasis"><em>works</em></span> 52436ac495dSmrg except for some corner cases. Support for localization 52536ac495dSmrg in <code class="classname">locale</code> may be incomplete on some non-GNU 52636ac495dSmrg platforms. Also dependent on the underlying platform is support 52736ac495dSmrg for <span class="type">wchar_t</span> and <span class="type">long long</span> specializations, 52836ac495dSmrg and details of thread support. 52936ac495dSmrg </p><p> 53036ac495dSmrg Long answer: See the implementation status pages for 53136ac495dSmrg <a class="link" href="manual/status.html#status.iso.1998" title="C++ 1998/2003">C++98</a>, 53236ac495dSmrg <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">TR1</a>, 53336ac495dSmrg <a class="link" href="manual/status.html#status.iso.2011" title="C++ 2011">C++11</a>, 53436ac495dSmrg <a class="link" href="manual/status.html#status.iso.2014" title="C++ 2014">C++14</a>, and 53536ac495dSmrg <a class="link" href="manual/status.html#status.iso.2017" title="C++ 2017">C++17</a>. 53636ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.standard_bugs"></a><a id="q-standard_bugs"></a><p><strong>5.2.</strong></p></td><td align="left" valign="top"><p> 53736ac495dSmrg Bugs in the ISO C++ language or library specification 53836ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-standard_bugs"></a></td><td align="left" valign="top"><p> 53936ac495dSmrg Unfortunately, there are some. 54036ac495dSmrg </p><p> 54136ac495dSmrg For those people who are not part of the ISO Library Group 54236ac495dSmrg (i.e., nearly all of us needing to read this page in the first 54336ac495dSmrg place), a public list of the library defects is occasionally 54436ac495dSmrg published on <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/" target="_top">the WG21 54536ac495dSmrg website</a>. 546a2dc1f3fSmrg Many of these issues have resulted in 547a2dc1f3fSmrg <a class="link" href="manual/bugs.html#manual.intro.status.bugs.iso" title="Standard Bugs">code changes in libstdc++</a>. 54836ac495dSmrg </p><p> 54936ac495dSmrg If you think you've discovered a new bug that is not listed, 55036ac495dSmrg please post a message describing your problem to the author of 55136ac495dSmrg the library issues list. 55236ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.compiler_bugs"></a><a id="q-compiler_bugs"></a><p><strong>5.3.</strong></p></td><td align="left" valign="top"><p> 55336ac495dSmrg Bugs in the compiler (gcc/g++) and not libstdc++ 55436ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-compiler_bugs"></a></td><td align="left" valign="top"><p> 55536ac495dSmrg On occasion, the compiler is wrong. Please be advised that this 55636ac495dSmrg happens much less often than one would think, and avoid jumping to 55736ac495dSmrg conclusions. 55836ac495dSmrg </p><p> 55936ac495dSmrg First, examine the ISO C++ standard. Second, try another compiler 56036ac495dSmrg or an older version of the GNU compilers. Third, you can find more 56136ac495dSmrg information on the libstdc++ and the GCC mailing lists: search 56236ac495dSmrg these lists with terms describing your issue. 56336ac495dSmrg </p><p> 56436ac495dSmrg Before reporting a bug, please examine the 565a2dc1f3fSmrg <a class="link" href="https://gcc.gnu.org/bugs/" target="_top">bugs database</a>, with the 566a2dc1f3fSmrg component set to <span class="quote">“<span class="quote">c++</span>”</span>. 56736ac495dSmrg </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>6.1. <a href="faq.html#faq.stream_reopening_fails"> 56836ac495dSmrg Reopening a stream fails 56936ac495dSmrg </a></dt><dt>6.2. <a href="faq.html#faq.wefcxx_verbose"> 57036ac495dSmrg -Weffc++ complains too much 57136ac495dSmrg </a></dt><dt>6.3. <a href="faq.html#faq.ambiguous_overloads"> 57236ac495dSmrg Ambiguous overloads after including an old-style header 57336ac495dSmrg </a></dt><dt>6.4. <a href="faq.html#faq.v2_headers"> 57436ac495dSmrg The g++-3 headers are not ours 57536ac495dSmrg </a></dt><dt>6.5. <a href="faq.html#faq.boost_concept_checks"> 57636ac495dSmrg Errors about *Concept and 57736ac495dSmrg constraints in the STL 57836ac495dSmrg </a></dt><dt>6.6. <a href="faq.html#faq.dlopen_crash"> 57936ac495dSmrg Program crashes when using library code in a 58036ac495dSmrg dynamically-loaded library 58136ac495dSmrg </a></dt><dt>6.7. <a href="faq.html#faq.memory_leaks"> 582a2dc1f3fSmrg “Memory leaks” in libstdc++ 58336ac495dSmrg </a></dt><dt>6.8. <a href="faq.html#faq.list_size_on"> 58436ac495dSmrg list::size() is O(n)! 58536ac495dSmrg </a></dt><dt>6.9. <a href="faq.html#faq.easy_to_fix"> 58636ac495dSmrg Aw, that's easy to fix! 58736ac495dSmrg </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.stream_reopening_fails"></a><a id="q-stream_reopening_fails"></a><p><strong>6.1.</strong></p></td><td align="left" valign="top"><p> 58836ac495dSmrg Reopening a stream fails 589a2dc1f3fSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-stream_reopening_fails"></a></td><td align="left" valign="top"><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This answer is old and probably no longer be relevant.</p></div><p> 590a2dc1f3fSmrg Prior to GCC 4.0 this was one of the most-reported non-bug reports. 591a2dc1f3fSmrg Executing a sequence like this would fail: 59236ac495dSmrg </p><pre class="programlisting"> 59336ac495dSmrg #include <fstream> 59436ac495dSmrg ... 59536ac495dSmrg std::fstream fs("a_file"); 59636ac495dSmrg // . 59736ac495dSmrg // . do things with fs... 59836ac495dSmrg // . 59936ac495dSmrg fs.close(); 60036ac495dSmrg fs.open("a_new_file"); 60136ac495dSmrg </pre><p> 602a2dc1f3fSmrg All operations on the re-opened <code class="varname">fs</code> would fail, or at 603a2dc1f3fSmrg least act very strangely, especially if <code class="varname">fs</code> reached the 604a2dc1f3fSmrg EOF state on the previous file. 605a2dc1f3fSmrg The original C++98 standard did not specify behavior in this case, and 606a2dc1f3fSmrg the <a class="link" href="manual/bugs.html#manual.bugs.dr22">resolution of DR #22</a> was to 607a2dc1f3fSmrg leave the state flags unchanged on a successful call to 608a2dc1f3fSmrg <code class="function">open()</code>. 609a2dc1f3fSmrg You had to insert a call to <code class="function">fs.clear()</code> between the 610a2dc1f3fSmrg calls to <code class="function">close()</code> and <code class="function">open()</code>, 611a2dc1f3fSmrg and then everything will work as expected. 612a2dc1f3fSmrg <span class="emphasis"><em>Update:</em></span> For GCC 4.0 we implemented the resolution 613a2dc1f3fSmrg of <a class="link" href="manual/bugs.html#manual.bugs.dr409">DR #409</a> and 614a2dc1f3fSmrg <code class="function">open()</code> 615a2dc1f3fSmrg now calls <code class="function">clear()</code> on success. 61636ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.wefcxx_verbose"></a><a id="q-wefcxx_verbose"></a><p><strong>6.2.</strong></p></td><td align="left" valign="top"><p> 61736ac495dSmrg -Weffc++ complains too much 61836ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-wefcxx_verbose"></a></td><td align="left" valign="top"><p> 61936ac495dSmrg Many warnings are emitted when <code class="option">-Weffc++</code> is used. Making 62036ac495dSmrg libstdc++ <code class="option">-Weffc++</code>-clean is not a goal of the project, 62136ac495dSmrg for a few reasons. Mainly, that option tries to enforce 62236ac495dSmrg object-oriented programming, while the Standard Library isn't 623a2dc1f3fSmrg necessarily trying to be OO. The option also enforces outdated guidelines 624a2dc1f3fSmrg from old editions of the books, and the advice isn't all relevant to 625a2dc1f3fSmrg modern C++ (especially C++11 and later). 62636ac495dSmrg </p><p> 62736ac495dSmrg We do, however, try to have libstdc++ sources as clean as possible. If 62836ac495dSmrg you see some simple changes that pacify <code class="option">-Weffc++</code> 62936ac495dSmrg without other drawbacks, send us a patch. 63036ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.ambiguous_overloads"></a><a id="q-ambiguous_overloads"></a><p><strong>6.3.</strong></p></td><td align="left" valign="top"><p> 63136ac495dSmrg Ambiguous overloads after including an old-style header 63236ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-ambiguous_overloads"></a></td><td align="left" valign="top"><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This answer is old and probably no longer be relevant.</p></div><p> 63336ac495dSmrg Another problem is the <code class="literal">rel_ops</code> namespace and the template 63436ac495dSmrg comparison operator functions contained therein. If they become 63536ac495dSmrg visible in the same namespace as other comparison functions 636a2dc1f3fSmrg (e.g., <span class="quote">“<span class="quote">using</span>”</span> them and the 637a2dc1f3fSmrg <code class="filename"><iterator></code> header), 63836ac495dSmrg then you will suddenly be faced with huge numbers of ambiguity 639a2dc1f3fSmrg errors. This was discussed on the mailing list; Nathan Myers 64036ac495dSmrg <a class="link" href="http://gcc.gnu.org/ml/libstdc++/2001-01/msg00247.html" target="_top">sums 64136ac495dSmrg things up here</a>. The collisions with vector/string iterator 64236ac495dSmrg types have been fixed for 3.1. 64336ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.v2_headers"></a><a id="q-v2_headers"></a><p><strong>6.4.</strong></p></td><td align="left" valign="top"><p> 64436ac495dSmrg The g++-3 headers are <span class="emphasis"><em>not ours</em></span> 645a2dc1f3fSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-v2_headers"></a></td><td align="left" valign="top"><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This answer is old and probably no longer be relevant.</p></div><p> 64636ac495dSmrg If you are using headers in 64736ac495dSmrg <code class="filename">${prefix}/include/g++-3</code>, or if 64836ac495dSmrg the installed library's name looks like 64936ac495dSmrg <code class="filename">libstdc++-2.10.a</code> or 65036ac495dSmrg <code class="filename">libstdc++-libc6-2.10.so</code>, then 65136ac495dSmrg you are using the old libstdc++-v2 library, which is non-standard and 65236ac495dSmrg unmaintained. Do not report problems with -v2 to the -v3 65336ac495dSmrg mailing list. 65436ac495dSmrg </p><p> 65536ac495dSmrg For GCC versions 3.0 and 3.1 the libstdc++ header files are installed in 65636ac495dSmrg <code class="filename">${prefix}/include/g++-v3</code> 65736ac495dSmrg (see the 'v'?). Starting with version 3.2 the headers are installed in 65836ac495dSmrg <code class="filename">${prefix}/include/c++/${version}</code> 65936ac495dSmrg as this prevents headers from previous versions being found by mistake. 66036ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.boost_concept_checks"></a><a id="q-boost_concept_checks"></a><p><strong>6.5.</strong></p></td><td align="left" valign="top"><p> 66136ac495dSmrg Errors about <span class="emphasis"><em>*Concept</em></span> and 66236ac495dSmrg <span class="emphasis"><em>constraints</em></span> in the STL 66336ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-boost_concept_checks"></a></td><td align="left" valign="top"><p> 66436ac495dSmrg If you see compilation errors containing messages about 66536ac495dSmrg <span class="errortext">foo Concept</span> and something to do with a 66636ac495dSmrg <span class="errortext">constraints</span> member function, then most 66736ac495dSmrg likely you have violated one of the requirements for types used 66836ac495dSmrg during instantiation of template containers and functions. For 66936ac495dSmrg example, EqualityComparableConcept appears if your types must be 67036ac495dSmrg comparable with == and you have not provided this capability (a 67136ac495dSmrg typo, or wrong visibility, or you just plain forgot, etc). 67236ac495dSmrg </p><p> 67336ac495dSmrg More information, including how to optionally enable/disable the 67436ac495dSmrg checks, is available in the 67536ac495dSmrg <a class="link" href="manual/concept_checking.html" title="Concept Checking">Diagnostics</a>. 67636ac495dSmrg chapter of the manual. 67736ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.dlopen_crash"></a><a id="q-dlopen_crash"></a><p><strong>6.6.</strong></p></td><td align="left" valign="top"><p> 67836ac495dSmrg Program crashes when using library code in a 67936ac495dSmrg dynamically-loaded library 68036ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-dlopen_crash"></a></td><td align="left" valign="top"><p> 68136ac495dSmrg If you are using the C++ library across dynamically-loaded 68236ac495dSmrg objects, make certain that you are passing the correct options 68336ac495dSmrg when compiling and linking: 68436ac495dSmrg </p><div class="literallayout"><p><br /> 68536ac495dSmrg Compile your library components:<br /> 68636ac495dSmrg <span class="command"><strong>g++ -fPIC -c a.cc</strong></span><br /> 68736ac495dSmrg <span class="command"><strong>g++ -fPIC -c b.cc</strong></span><br /> 68836ac495dSmrg ...<br /> 68936ac495dSmrg <span class="command"><strong>g++ -fPIC -c z.cc</strong></span><br /> 69036ac495dSmrg<br /> 69136ac495dSmrg Create your library:<br /> 69236ac495dSmrg <span class="command"><strong>g++ -fPIC -shared -rdynamic -o libfoo.so a.o b.o ... z.o</strong></span><br /> 69336ac495dSmrg<br /> 69436ac495dSmrg Link the executable:<br /> 69536ac495dSmrg <span class="command"><strong>g++ -fPIC -rdynamic -o foo ... -L. -lfoo -ldl</strong></span><br /> 69636ac495dSmrg </p></div></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.memory_leaks"></a><a id="q-memory_leaks"></a><p><strong>6.7.</strong></p></td><td align="left" valign="top"><p> 697a2dc1f3fSmrg <span class="quote">“<span class="quote">Memory leaks</span>”</span> in libstdc++ 69836ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-memory_leaks"></a></td><td align="left" valign="top"><p> 699a2dc1f3fSmrg Since GCC 5.1.0, libstdc++ automatically allocates a pool 700a2dc1f3fSmrg of a few dozen kilobytes on startup. This pool is used to ensure it's 701a2dc1f3fSmrg possible to throw exceptions (such as <code class="classname">bad_alloc</code>) 702a2dc1f3fSmrg even when <code class="code">malloc</code> is unable to allocate any more memory. 703a2dc1f3fSmrg With some versions of <a class="link" href="http://valgrind.org/" target="_top"><span class="command"><strong>valgrind</strong></span></a> 704a2dc1f3fSmrg this pool will be shown as "still reachable" when the process exits, e.g. 705a2dc1f3fSmrg <code class="code">still reachable: 72,704 bytes in 1 blocks</code>. 706a2dc1f3fSmrg This memory is not a leak, because it's still in use by libstdc++, 707a2dc1f3fSmrg and the memory will be returned to the OS when the process exits. 708a2dc1f3fSmrg Later versions of <span class="command"><strong>valgrind</strong></span> know how to free this 709a2dc1f3fSmrg pool as the process exits, and so won't show any "still reachable" memory. 710a2dc1f3fSmrg </p><p> 711a2dc1f3fSmrg In the past, a few people reported that the standard containers appear 71236ac495dSmrg to leak memory when tested with memory checkers such as 71336ac495dSmrg <a class="link" href="http://valgrind.org/" target="_top"><span class="command"><strong>valgrind</strong></span></a>. 714a2dc1f3fSmrg Under some (non-default) configurations the library's allocators keep 715a2dc1f3fSmrg free memory in a 716a2dc1f3fSmrg pool for later reuse, rather than deallocating it with <code class="code">delete</code> 717a2dc1f3fSmrg Although this memory is always reachable by the library and is never 71836ac495dSmrg lost, memory debugging tools can report it as a leak. If you 71936ac495dSmrg want to test the library for memory leaks please read 72036ac495dSmrg <a class="link" href="manual/debug.html#debug.memory" title="Memory Leak Hunting">Tips for memory leak hunting</a> 72136ac495dSmrg first. 72236ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.list_size_on"></a><a id="q-list_size_on"></a><p><strong>6.8.</strong></p></td><td align="left" valign="top"><p> 723a2dc1f3fSmrg <code class="code">list::size()</code> is O(n)! 72436ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-list_size_on"></a></td><td align="left" valign="top"><p> 72536ac495dSmrg See 72636ac495dSmrg the <a class="link" href="manual/containers.html" title="Chapter 9. Containers">Containers</a> 72736ac495dSmrg chapter. 72836ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.easy_to_fix"></a><a id="q-easy_to_fix"></a><p><strong>6.9.</strong></p></td><td align="left" valign="top"><p> 72936ac495dSmrg Aw, that's easy to fix! 73036ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-easy_to_fix"></a></td><td align="left" valign="top"><p> 73136ac495dSmrg If you have found a bug in the library and you think you have 73236ac495dSmrg a working fix, then send it in! The main GCC site has a page 73336ac495dSmrg on <a class="link" href="http://gcc.gnu.org/contribute.html" target="_top">submitting 73436ac495dSmrg patches</a> that covers the procedure, but for libstdc++ you 73536ac495dSmrg should also send the patch to our mailing list in addition to 73636ac495dSmrg the GCC patches mailing list. The libstdc++ 73736ac495dSmrg <a class="link" href="manual/appendix_contributing.html" title="Appendix A. Contributing">contributors' page</a> 73836ac495dSmrg also talks about how to submit patches. 73936ac495dSmrg </p><p> 74036ac495dSmrg In addition to the description, the patch, and the ChangeLog 74136ac495dSmrg entry, it is a Good Thing if you can additionally create a small 74236ac495dSmrg test program to test for the presence of the bug that your patch 74336ac495dSmrg fixes. Bugs have a way of being reintroduced; if an old bug 74436ac495dSmrg creeps back in, it will be caught immediately by the testsuite - 74536ac495dSmrg but only if such a test exists. 74636ac495dSmrg </p></td></tr><tr class="toc"><td align="left" valign="top" colspan="2"><dl><dt>7.1. <a href="faq.html#faq.iterator_as_pod"> 747a2dc1f3fSmrg string::iterator is not char*; 748a2dc1f3fSmrg vector<T>::iterator is not T* 74936ac495dSmrg </a></dt><dt>7.2. <a href="faq.html#faq.what_is_next"> 75036ac495dSmrg What's next after libstdc++? 75136ac495dSmrg </a></dt><dt>7.3. <a href="faq.html#faq.sgi_stl"> 75236ac495dSmrg What about the STL from SGI? 75336ac495dSmrg </a></dt><dt>7.4. <a href="faq.html#faq.extensions_and_backwards_compat"> 75436ac495dSmrg Extensions and Backward Compatibility 75536ac495dSmrg </a></dt><dt>7.5. <a href="faq.html#faq.tr1_support"> 75636ac495dSmrg Does libstdc++ support TR1? 75736ac495dSmrg </a></dt><dt>7.6. <a href="faq.html#faq.get_iso_cxx">How do I get a copy of the ISO C++ Standard? 75836ac495dSmrg </a></dt><dt>7.7. <a href="faq.html#faq.what_is_abi"> 75936ac495dSmrg What's an ABI and why is it so messy? 76036ac495dSmrg </a></dt><dt>7.8. <a href="faq.html#faq.size_equals_capacity"> 76136ac495dSmrg How do I make std::vector<T>::capacity() == std::vector<T>::size? 76236ac495dSmrg </a></dt></dl></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.iterator_as_pod"></a><a id="faq.iterator_as_pod_q"></a><p><strong>7.1.</strong></p></td><td align="left" valign="top"><p> 763a2dc1f3fSmrg <code class="classname">string::iterator</code> is not <code class="code">char*</code>; 764a2dc1f3fSmrg <code class="classname">vector<T>::iterator</code> is not <code class="code">T*</code> 76536ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="faq.iterator_as_pod_a"></a></td><td align="left" valign="top"><p> 76636ac495dSmrg If you have code that depends on container<T> iterators 76736ac495dSmrg being implemented as pointer-to-T, your code is broken. It's 76836ac495dSmrg considered a feature, not a bug, that libstdc++ points this out. 76936ac495dSmrg </p><p> 77036ac495dSmrg While there are arguments for iterators to be implemented in 77136ac495dSmrg that manner, A) they aren't very good ones in the long term, 77236ac495dSmrg and B) they were never guaranteed by the Standard anyway. The 77336ac495dSmrg type-safety achieved by making iterators a real class rather 77436ac495dSmrg than a typedef for <span class="type">T*</span> outweighs nearly all opposing 77536ac495dSmrg arguments. 77636ac495dSmrg </p><p> 777a2dc1f3fSmrg Code which does assume that a vector/string iterator <code class="varname">i</code> 77836ac495dSmrg is a pointer can often be fixed by changing <code class="varname">i</code> in 779a2dc1f3fSmrg certain expressions to <code class="varname">&*i</code>. 78036ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.what_is_next"></a><a id="q-what_is_next"></a><p><strong>7.2.</strong></p></td><td align="left" valign="top"><p> 78136ac495dSmrg What's next after libstdc++? 78236ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_is_next"></a></td><td align="left" valign="top"><p> 783a2dc1f3fSmrg The goal of libstdc++ is to produce a 784a2dc1f3fSmrg fully-compliant, fully-portable Standard Library. 785a2dc1f3fSmrg While the C++ Standard continues to evolve the libstdc++ will 786a2dc1f3fSmrg continue to track it. 78736ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.sgi_stl"></a><a id="q-sgi_stl"></a><p><strong>7.3.</strong></p></td><td align="left" valign="top"><p> 78836ac495dSmrg What about the STL from SGI? 78936ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-sgi_stl"></a></td><td align="left" valign="top"><p> 790a2dc1f3fSmrg The STL (Standard Template Library) was the inspiration for large chunks 791a2dc1f3fSmrg of the C++ Standard Library, but the terms are not interchangeable and 792a2dc1f3fSmrg they don't mean the same thing. The C++ Standard Library includes lots of 793a2dc1f3fSmrg things that didn't come from the STL, and some of them aren't even 794a2dc1f3fSmrg templates, such as <code class="classname">std::locale</code> and 795a2dc1f3fSmrg <code class="classname">std::thread</code>. 796a2dc1f3fSmrg </p><p> 797a2dc1f3fSmrg Libstdc++-v3 incorporates a lot of code from 798a2dc1f3fSmrg <a class="link" href="https://web.archive.org/web/20171225062613/http://www.sgi.com/tech/stl/" target="_top">the SGI STL</a> 799a2dc1f3fSmrg (the final merge was from 800a2dc1f3fSmrg <a class="link" href="https://web.archive.org/web/20171225062613/http://www.sgi.com/tech/stl/whats_new.html" target="_top">release 3.3</a>). 801a2dc1f3fSmrg The code in libstdc++ contains many fixes and changes compared to the 802a2dc1f3fSmrg original SGI code. 80336ac495dSmrg </p><p> 80436ac495dSmrg In particular, <code class="classname">string</code> is not from SGI and makes no 805a2dc1f3fSmrg use of their "rope" class (although that is included as an optional 806a2dc1f3fSmrg extension), neither is <code class="classname">valarray</code> nor some others. 807a2dc1f3fSmrg Classes like <code class="classname">vector<></code> were from SGI, but have 808a2dc1f3fSmrg been extensively modified. 80936ac495dSmrg </p><p> 81036ac495dSmrg More information on the evolution of libstdc++ can be found at the 81136ac495dSmrg <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">API 81236ac495dSmrg evolution</a> 81336ac495dSmrg and <a class="link" href="manual/backwards.html" title="Backwards Compatibility">backwards 81436ac495dSmrg compatibility</a> documentation. 81536ac495dSmrg </p><p> 816*8feb0f0bSmrg The <a class="link" href="https://web.archive.org/web/20171104092813/http://www.sgi.com/tech/stl/FAQ.html" target="_top">FAQ</a> 81736ac495dSmrg for SGI's STL is still recommended reading. 81836ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.extensions_and_backwards_compat"></a><a id="q-extensions_and_backwards_compat"></a><p><strong>7.4.</strong></p></td><td align="left" valign="top"><p> 81936ac495dSmrg Extensions and Backward Compatibility 82036ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-extensions_and_backwards_compat"></a></td><td align="left" valign="top"><p> 82136ac495dSmrg See the <a class="link" href="manual/backwards.html" title="Backwards Compatibility">link</a> on backwards compatibility and <a class="link" href="manual/api.html" title="API Evolution and Deprecation History">link</a> on evolution. 82236ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.tr1_support"></a><a id="q-tr1_support"></a><p><strong>7.5.</strong></p></td><td align="left" valign="top"><p> 82336ac495dSmrg Does libstdc++ support TR1? 82436ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-tr1_support"></a></td><td align="left" valign="top"><p> 82536ac495dSmrg Yes. 82636ac495dSmrg </p><p> 827a2dc1f3fSmrg The C++ Standard Library 82836ac495dSmrg <a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top"> 829a2dc1f3fSmrg Technical Report 1</a> added many new features to the library. 83036ac495dSmrg </p><p> 831a2dc1f3fSmrg The implementation status of TR1 in libstdc++ can be tracked 832a2dc1f3fSmrg <a class="link" href="manual/status.html#status.iso.tr1" title="C++ TR1">on the TR1 status page</a>. 833a2dc1f3fSmrg </p><p> 834a2dc1f3fSmrg New code should probably not use TR1, because almost everything in it has 835a2dc1f3fSmrg been added to the main C++ Standard Library (usually with significant 836a2dc1f3fSmrg improvements). 837a2dc1f3fSmrg The TR1 implementation in libstdc++ is no longer actively maintained. 83836ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.get_iso_cxx"></a><a id="q-get_iso_cxx"></a><p><strong>7.6.</strong></p></td><td align="left" valign="top"><p>How do I get a copy of the ISO C++ Standard? 83936ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-get_iso_cxx"></a></td><td align="left" valign="top"><p> 84036ac495dSmrg Please refer to the <a class="link" href="manual/appendix_contributing.html" title="Appendix A. Contributing">Contributing</a> 84136ac495dSmrg section in our manual. 84236ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.what_is_abi"></a><a id="q-what_is_abi"></a><p><strong>7.7.</strong></p></td><td align="left" valign="top"><p> 84336ac495dSmrg What's an ABI and why is it so messy? 84436ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-what_is_abi"></a></td><td align="left" valign="top"><p> 84536ac495dSmrg <acronym class="acronym">ABI</acronym> stands for <span class="quote">“<span class="quote">Application Binary 84636ac495dSmrg Interface</span>”</span>. Conventionally, it refers to a great 84736ac495dSmrg mass of details about how arguments are arranged on the call 84836ac495dSmrg stack and/or in registers, and how various types are arranged 84936ac495dSmrg and padded in structs. A single CPU design may suffer 85036ac495dSmrg multiple ABIs designed by different development tool vendors 85136ac495dSmrg who made different choices, or even by the same vendor for 85236ac495dSmrg different target applications or compiler versions. In ideal 85336ac495dSmrg circumstances the CPU designer presents one ABI and all the 85436ac495dSmrg OSes and compilers use it. In practice every ABI omits 85536ac495dSmrg details that compiler implementers (consciously or 85636ac495dSmrg accidentally) must choose for themselves. 85736ac495dSmrg </p><p> 85836ac495dSmrg That ABI definition suffices for compilers to generate code so a 85936ac495dSmrg program can interact safely with an OS and its lowest-level libraries. 86036ac495dSmrg Users usually want an ABI to encompass more detail, allowing libraries 86136ac495dSmrg built with different compilers (or different releases of the same 86236ac495dSmrg compiler!) to be linked together. For C++, this includes many more 86336ac495dSmrg details than for C, and most CPU designers (for good reasons elaborated 86436ac495dSmrg below) have not stepped up to publish C++ ABIs. Such an ABI has been 86536ac495dSmrg defined for the Itanium architecture (see 86636ac495dSmrg <a class="link" href="https://itanium-cxx-abi.github.io/cxx-abi/" target="_top">C++ 86736ac495dSmrg ABI for Itanium</a>) and that is used by G++ and other compilers 86836ac495dSmrg as the de facto standard ABI on many common architectures (including x86). 86936ac495dSmrg G++ can also use the ARM architecture's EABI, for embedded 87036ac495dSmrg systems relying only on a <span class="quote">“<span class="quote">free-standing implementation</span>”</span> that 87136ac495dSmrg doesn't include (much of) the standard library, and the GNU EABI for 87236ac495dSmrg hosted implementations on ARM. Those ABIs cover low-level details 87336ac495dSmrg such as virtual function implementation, struct inheritance layout, 87436ac495dSmrg name mangling, and exception handling. 87536ac495dSmrg </p><p> 87636ac495dSmrg A useful C++ ABI must also incorporate many details of the standard 87736ac495dSmrg library implementation. For a C ABI, the layouts of a few structs 87836ac495dSmrg (such as <span class="type">FILE</span>, <span class="type">stat</span>, <span class="type">jmpbuf</span>, 87936ac495dSmrg and the like) and a few macros suffice. 88036ac495dSmrg For C++, the details include the complete set of names of functions 88136ac495dSmrg and types used, the offsets of class members and virtual functions, 88236ac495dSmrg and the actual definitions of all inlines. C++ exposes many more 88336ac495dSmrg library details to the caller than C does. It makes defining 88436ac495dSmrg a complete ABI a much bigger undertaking, and requires not just 88536ac495dSmrg documenting library implementation details, but carefully designing 88636ac495dSmrg those details so that future bug fixes and optimizations don't 88736ac495dSmrg force breaking the ABI. 88836ac495dSmrg </p><p> 88936ac495dSmrg There are ways to help isolate library implementation details from the 89036ac495dSmrg ABI, but they trade off against speed. Library details used in inner 89136ac495dSmrg loops (e.g., <code class="function">getchar</code>) must be exposed and frozen for 89236ac495dSmrg all time, but many others may reasonably be kept hidden from user code, 89336ac495dSmrg so they may later be changed. Deciding which, and implementing 89436ac495dSmrg the decisions, must happen before you can reasonably document a 89536ac495dSmrg candidate C++ ABI that encompasses the standard library. 89636ac495dSmrg </p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.size_equals_capacity"></a><a id="q-size_equals_capacity"></a><p><strong>7.8.</strong></p></td><td align="left" valign="top"><p> 897a2dc1f3fSmrg How do I make <code class="code">std::vector<T>::capacity() == std::vector<T>::size</code>? 89836ac495dSmrg </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-size_equals_capacity"></a></td><td align="left" valign="top"><p> 899a2dc1f3fSmrg Since C++11 just call the <code class="function">shrink_to_fit()</code> member 900a2dc1f3fSmrg function. 901a2dc1f3fSmrg </p><p> 902a2dc1f3fSmrg Before C++11, the standard idiom for deallocating a 903a2dc1f3fSmrg <code class="classname">vector<T></code>'s 904a2dc1f3fSmrg unused memory was to create a temporary copy of the vector and swap their 90536ac495dSmrg contents, e.g. for <code class="classname">vector<T> v</code> 90636ac495dSmrg </p><div class="literallayout"><p><br /> 90736ac495dSmrg std::vector<T>(v).swap(v);<br /> 90836ac495dSmrg </p></div><p> 90936ac495dSmrg The copy will take O(n) time and the swap is constant time. 91036ac495dSmrg </p><p> 91136ac495dSmrg See <a class="link" href="manual/strings.html#strings.string.shrink" title="Shrink to Fit">Shrink-to-fit 91236ac495dSmrg strings</a> for a similar solution for strings. 91336ac495dSmrg </p></td></tr></tbody></table></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bk03.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="bk03.html">Up</a></td><td width="40%" align="right"> </td></tr><tr><td width="40%" align="left" valign="top"> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> </td></tr></table></div></body></html>